Years ago I was the only person staying at a state campground, the last week before they closed for the winter. I had my pick of campsites, as I was setting up my tent I noticed a big dead yellow birch so decided to move. I was eating supper when I heard a "crash" then what sounded like water running. The tree had fallen over, breaking an above-ground water line. There wasn't a breath of wind, it was just that tree's time to go. Had I taken the attitude that it wouldn't happen to me, I would have been right in the fall zone. An ounce of prevention is worth a pound of cure... and keeps your local tree surgeon in business.